Composite lenses

ABSTRACT

A lens of large diameter and short focal length comprises a plurality of interengageable elements which are moulded in a transparent material, or in transparent materials having the same refractive index. The elements are interengaged to constitute the required lens.

I United States [111 3,5 0,

[72] Inventor Harris Vern. 350/189,

Llchtleld. England 211.213.233.234, H5, 178 [2]] Appl. No.- 758,855 22Filed Sept. 10, 1968 References Cited [45] Patented May 25, 1971 UNITEDSTATES PATENTS [73] Assignee Joseph Lucas (Industries) Li i 2,175,51810/1939 Djian 350/223X 2,908,209 10/1959 Marvin et 31.. 3s0/175ux 222322 3,049,054 8/1962 Waland 3s0/179ux 3 3,182,576 5/l965 Papke 350/2l lXPrimary Examiner-John K. Corbin Attorney-Holman and Stem [54] COMPOSITELENSES 6 Claims 4 Drawmg Figs ABSTRACT: A lens of large diameter andshort focal length [52] U.S.Cl 350/189, comprises a plurality ofinterengageable elements which are 350/ 178, 350/21 1, 350/234 mouldedin a transparent material, or in transparent materials [51] Int. Cl G02b3/04, having the same refractive index. The elements are in- G02b 3/08,G02b 9/02 terengaged to constitute the required lens.

PATENTEDHAY25|97| 3580.663

SHEET 2 OF 3 ATTORNEYS COMPOSITE LENSES This invention relates to lensesof large diameter and short focal length.

A conventional lens having a large diameter and a short focal lengthnecessarily has a large axial thickness. When such a lens is moulded,owing to the large volume of material at the central portion of the lensshrinkage and consequential distortion of the central portion of thelens occurs.

it is an object of the present invention to provide a lens of largediameter and short focal length wherein the danger of distortion of thelens due to shrinkage during manufacture is minimized.

A lens according to the invention comprises a plurality ofinterengageable elements mounded in a transparent material or intransparent materials having the same refractive index, the elementsbeing interengaged to constitute the required lens.

In the accompanying drawings,

FIG. I is a sectional view of a lens according to one example of theinvention,

FIG. 2 is a sectional view ofa modification of the lens shown in FIG. 1,

FIG. Sis a sectional view of a lens combination utilizing a lens asshown in FIG. I, and

FIG. 4 is a sectional view of lens combination utilizing a pair oflenses as shown in FIG. 1.

Referring first to FIG. I of the drawings, the lens includes a firstelement 11 moulded in a transparent synthetic resin material and havinga part spherical concave surface 12. Engaged with the surface 12 of theelement II is a complementarily shaped convex surface 14 of a secondelement 13. The element 13 is moulded in the same material as theelement 11 and includes a surface 15 parallel with the surface 14.Engaged with the surface 15 of the element 13 is a third element 16similar to the element 13 but smaller than the element 13 and similarlyengaged with the element 16 is a fourth element 17 similar to theelement 16 but smaller than the element I6. Engaged with the concavesurface 18 of the element I7 is a complementarily shaped convex surface21 of a fifth element 19. The element 19 is moulded in the same materialas the other four elements and has a convex surface 22 opposite thesurface 21. The peripheral surfaces Ilal3al6aancl l7aof the elements 11,I3, 16 and I7 and the surface 22 of the element 19 are such that theyconstitute a part spherical surface of the lens, the other surface ofthe lens being the surface 23 of the element 11. The surface 23 is soshaped that the lens is aspherical, that is to say the lens exhibitsminimal spherical aberration.

In order to eliminate air gaps between the elements I], I3, l6, l7 and19 which would lower the coefficient of transmission of the lens, themating surfaces of the elements are coated with a transparent liquidwhich fills the air gaps when the elements are interengaged. The liquidhas substantially the same coefficient of refraction as the material ormaterials in which the elements are moulded. A suitable liquid forexample is supplied by Midland Silicones Ltd., under their code No. M.S.200. and an alternative liquid is a silicone encapsulant, also sold byMidland Silicones Ltd., under their code No. DR 2628.

It will be appreciated that since each of the elements has a small axialthickness they can be moulded substantially without distortion owing toshrinkage.

The elements can be held together by a metal shell which also serves amounting means for the lens in use, the surface tension effects of theliquid between the elements aiding the action of the shell inmaintaining the elements in engagement.

In the modification shown in FIG. 2 the outer element I9 is formed withan integral, peripheral, axially extending wall 24 with which theperipheries of the elements 11, I3, 16 and 17 are engaged and theelements ll, 13, I6 and 17 are not of constant thickness. The wall 24serves to locate the elements ll, 13, I6 and 17 in their correctpositions and relieves the necessity of shaping the peripheral surfacesof the elements to constitute part of the optical surface of the lens.

In a further modification shown in dotted lines in FIG. I the element 11is moulded with an integral rod 20 extending axially from its surfaceI2, and each of the elements I3, I6, 17, I9, is moulded with an axialbore, the elements !3, 16, I7, I9 being threaded onto the rod of theelement 11 to assemble the lens.

As described above, the surfaces of the elements of the lenses can beparallel so that the elements are of constant thickness or the elementscan be so shaped that their thickness adjacent their peripheries isdifferent to their thickness adjacent their peripheral axes. The shapesof the elements is dependent upon the properties of the lens to beproduced. Provided that the difference between the axial thickness andthe peripheral thickness of the elements is not too great, then theelements can be moulded substantially without shrinkage and distortion.

A large diameter, short focal length, aspherical lens as described abovecan be used as one of the outer elements of a three element achromaticlens combination. In one example of such an achromatic lens combination,as shown in FIG. 3,

the individual elements ll, 13, 16, I7, I9 of the aspherical lens aremoulded in transparent polymethylmethacrylate and are assembled. Theother outer element 25 of the achromatic lens is also moulded inpolymethylmethacrylate, but in the form of an echelon lens, andsandwiched between the two outer elements is an inner element 26 mouldedin transparent polystyrene generally in the form of a concave lens, onesurface of the inner element 26 being complementary to the surface 119,13a, 16a, 17a, 22 of the aspherical lens and the 0pposite surface of theinner element 26 being complementary to the convex surface of theechelon lens 25.

The dispersive powers of polymethylmethacrylate and polystyrene aresufficiently different that assuming that the focal lengths of the threeelements are correctly proportionate to one another then the lenscombination will be achromatic.

It will be appreciated that both outer elements of a three elementachromatic lens combination could be constituted by large diameter shortfocal length aspherical lenses as described above, such a lenscombination being shown in FIG. 4, and wherein the two lensesconstituting the outer elements are moulded in polymethylmethacrylateand the lens constituting the inner element 26 is moulded in polystrene.

In the two achromatic lens combinations described above the matingsurfaces of the lenses are coated with the liquid M.S. 200 or theencapsulant DR 2628 to eliminate air gaps between the lenses.

Iclaim:

I. An improved composite lens of short focal length and large diametercomprising a plurality of interengageable elements moulded in atransparent material, or in transparent materials having the samerefractive index, the elements being interengaged to constitute therequired lens, and

axially extending location means integral with one of saidinterengageable elements and engageable with the other elements tolocate said other element in the desired position with respect to saidone element, said means comprising a rod integral with one of said outerelements of the outer elements of the lens and extending through theremaining elements.

2. A lens as claimed in claim 1 wherein the mating surfaces of theelements are coated with a substance which eliminates air gaps betweensaid mating surfaces without materially affecting the optical propertiesof the lens.

3. A lens as claimed in claim I wherein one of the outer surfaces of thelens is shaped to render the lens aspherical.

4. An achromatic lens combination utilizing a lens as claimed in claim Ias one of the outer elements of the lens combination.

5. A lens combination as claimed in claim 4 wherein the other outerelement is constituted by a moulded echelon lens.

6. An achromatic lens combination utilizing a pair of lenses as claimedin claim I as the two outer elements of the lens combination.

1. An improved composite lens of short focal length and large diametercomprising a plurality of interengageable elements moulded in atransparent material, or in transparent materials having the samerefractive index, the elements being interengaged to constitute therequired lens, and axially extending location means integral with one ofsaid interengageable elements and engageable with the other elements tolocate Said other element in the desired position with respect to saidone element, said means comprising a rod integral with one of said outerelements of the outer elements of the lens and extending through theremaining elements.
 2. A lens as claimed in claim 1 wherein the matingsurfaces of the elements are coated with a substance which eliminatesair gaps between said mating surfaces without materially affecting theoptical properties of the lens.
 3. A lens as claimed in claim 1 whereinone of the outer surfaces of the lens is shaped to render the lensaspherical.
 4. An achromatic lens combination utilizing a lens asclaimed in claim 1 as one of the outer elements of the lens combination.5. A lens combination as claimed in claim 4 wherein the other outerelement is constituted by a moulded echelon lens.
 6. An achromatic lenscombination utilizing a pair of lenses as claimed in claim 1 as the twoouter elements of the lens combination.